Motion picture camera motor control

ABSTRACT

A motion picture camera with a rotary shutter which, as it rotates, periodically permits an image from the camera lens to reach the film, and then reflects the image to the eyepiece, etc. Motor controls are provided for controlling the speed of the shutter so that the shutter automatically stops at a location in which it blocks and reflects images to the eyepiece rather than one in which images are permitted to reach the film. A pulse generator operates synchronously with the rotary shutter. During stopping of the shutter, whenever the speed of the shutter is insufficient to bring it to a stop at the desired location, the pulse generator produces electrical pulses whose energy would decrease as the position of the shutter changes, but for the decrease in speed of the shutter, and these pulses are fed to the shutter drive motor to control its speed at a level sufficient to bring it to the desired location. Preferably, the pulse generator includes a transparent disc with opaque lines spaced around it, together with an infrared light source and a phototransistor. The spacing between adjacent opaque lines gradually decreases at successive positions around the disc, and a relatively large opaque area is provided on the disc in the vicinity of the position in which the shutter is to be stopped.

United States Patent Bauer, II

[54] MOTION PICTURE CAMERA MOTOR CONTROL [72] Inventor: George W. Bauer,1], Westfield, NJ. [73] Assignee: Anton Bauer, Inc., Norwalk, Conn.

[22] Filed: Dec. 14, 1970 [21] App]. No.: 97,545

[52] US. Cl. ..352/l76, 352/164, 352/180 [51] Int. Cl. ..G03b l/42 [58]Field of Search ..352/164, 165, 167, 169, 176,

[56] References Cited 7 UNITED STATES PATENTS 3,565,521 2/1971 Butler..352/180 X 3,326,626 6/1967 Floden ..352/ 169 3,236,581 2/1966 Mitchell..352/210 X 3,005,940 10/1961 Johnson ..318/313 X 3,154,730 10/1964l-louldin ..318/313 X 3,514,679 5/1970 Larsen ..318/313 X PrimaryExaminerSamuel S. Matthews Assistant Examiner-Monroe l-l. HayesAttorney-Curtis, Morris & Safford 51 Sept. 19, 1972 ABSTRACT A motionpicture camera with a rotary shutter which, as it rotates, periodicallypermits an image from the camera lens to reach the film, and thenreflects the image to the eyepiece, etc. Motor controls are provided forcontrolling the speed of the shutter so that the shutter automaticallystops at a location in which it blocks and reflects images to theeyepiece rather than one in which images are permitted to reach thefilm. A pulse generator operates synchronously with the rotary shutter.During stopping of the shutter, whenever the speed of the shutter isinsufficient to bring it to a stop at the desired location, the pulsegenerator produces electrical pulses whose energy would decrease as theposition of the shutter changes, but for the decrease in speed of theshutter, and these pulses are fed to the shutter drive motor to controlits speed at a level sufficient to bring it to the desired location.Preferably, the pulse generator includes a transparent disc with opaquelines spaced around it, together with an infrared light source and aphototransistor. The spacing between adjacent opaque lines graduallydecreases at successive positions around the disc, and a relativelylarge opaque area is provided on the disc in the vicinity of theposition in which the shutter is to be stopped.

PATENTED'SEP 19 I972 50 MOTOR CONTROL g wye WBaueljlI ATTUR Y5 MOTIONPICTURE CAMERA MOTOR CONTROL This invention relates to motor speedcontrol in motion picture cameras, and particularly to means forcontrolling the speed and stopping of a rotary shutter in a motionpicture camera.

In motion picture cameras utilizing rotary shutters, it is desired tostop the rotary shutter in a position in which it prevents images fromthe camera lens from reaching the film while the camera is inoperative.Furthermore, in such a camera in which the surface of the shutter whichintercepts the images is used to reflect the images to an eyepiece to beused by the cameraman for aiming the camera, it is desired that therotary shutter always be stopped in its reflecting position so that thecameraman can aim the camera in preparation for the next use of thecamera.

Accordingly, it is an object of the present invention to provide motionpicture motor speed control means, and particularly a device forautomatically stopping the rotary shutter of a motion picture camera sothat the images from the camera lens are directed to the eyepiece of thecamera instead of the film when the camera is not operating. A furtherobject of the present invention is to provide such a device which iscompact, light-weight, relatively easy to fabricate, and highly reliablein operation, and which performs with smoothness and rapidity so thatits operation is virtually unnoticeable by the operator.

In accordance with the present invention, the foregoing objects havebeen met by the provision of motion picture camera motor speed controlmeans in which the motor is energized by electrical signals whose energyis a function of the spacing between adjacent indicia on a rotor whichis driven by the motor, and of the speed of the rotor. This system isused to stop the camera shutter at a desired location by decreasing theenergy of the electrical signals as the shutter rotates in apre-determined direction. This position preferably is one in whichimages are prevented from reaching the film, and are instead reflectedto the eyepiece of the camera.

Further objects and advantages of the invention will be pointed out inor apparent from the following description and drawings. In thedrawings:

FIG. 1 is a partially broken away, partially schematic view of a portionof a camera constructed in accordance with the present invention;

FIG. 2 is a schematic perspective view of the principal components ofthe control system of the present invention;

FIG. 3 is a plan view of a component of a system shown in FIG. 2; and

FIG. 4 is a graph illustrating certain operational features of theinvention.

GENERAL OPERATION FIG. 1 illustrates a portion of a motion picturecamera with a housing 12 and a camera lens 14. A rotary reflectiveshutter 16 is mounted behind the lens 14. As is shown in FIG. 2, theshutter 16 is a disc with two opposite cut-out sectors 30, with twosectors 32 remaining. A film guide 18 guides motion picture film 20transversely through the optical path of the lens 14.

When either of the sectors 32 of the shutter 16 is positioned betweenthe lens 14 and the film 20, the images passing through the lens 14 areprevented from reaching the film. However, when the cut-out sectors 30move into the place of the sectors 32, the images are allowed to reachthe film.

The forward surfaces 22 (FIG. 1) of the sectors 32 are made reflectiveso that when they are positioned in the optical path between the lens 14and the film 20, the images are reflected downwardly to a reflectingprism 24, and then through a lens system 26 to the eyepiece 28 so thatthe cameraman can see the images for the purpose of aiming the camera.

Referring now to FIG. 2 as well as FIG. 1, the shutter 16 is mounted ona shaft 34 which is supported by suitable bearings (not shown). Theshutter 16 is rotated in the direction indicated by the arrow Y by a DCmotor 40 which drives a shaft 38 in the direction indicated by the arrowW. The shaft 38 drives the shaft 34 and the shutter 16 by means of a setof 45 helical gears 36. A shaft position indication disc 42 is securedto the shaft 38. The function of the disc 42 will be discussed ingreater detail below.

The electrical system which is shown in FIG. 2 is provided to drive theshutter at a constant speed when the camera is operating, and toautomatically stop the shutter in one of its blocking positions; thatis, a position in which one of the blocking sectors 32 reflects imagesto the eyepiece 28 rather than allowing them to reach the film.

The camera in which the present invention is used can be any of a numberof well-known motion picture cameras, preferably of professionalquality. An example of such a camera is the Arriflex 16 BL. Preferably,however, the invention is used together with the other advantageousfeatures of the camera shown in the co-pending U.S. patent applicationof Anton Wilson filed on Oct. 1, 1970 and entitled Motion PictureCamera. The disclosure of the later patent application hereby isincorporated herein by reference.

CONTROL SYSTEM OPERATION Referring to FIG. 2, a double-pole,double-throw camera switch 44 is provided. Both contact arms 46 and 48of the switch 44 are connected to a positive 12 volts DC power supplyfor the camera. When the switch 44 is turned ON, 12 volts DC is suppliedto one terminal 50 of the. motor 40 through the contact arm 48. The samevoltage is applied through contact arm 46, a conventional motor controlcircuit 52, and a diode 54 to the base of a transistor 56 whoseemittercollector path is connected between the other terminal of themotor 40 and ground. The motor control circuit 52 is conventional. Forexample, it includes a crystal oscillator to provide precise control ofthe speed of the motor 40.

SI-IU I IER DECELERATION CONTROL sufficient to ensure that the shutterwill coast all the way to the desired stopping location. Thus, if themotor speed is just right so that the shutter will coast to a stop atthe proper location, the control circuit does nothing. However, if thespeed is too low during the last revolution of the shutter, the controlcircuit will give it just enough acceleration to bring it to the properlocation.

Part of the deceleration control circuit is the disc 42. Only the edgeof the disc 42 is shown in FIG. 2, but the upper surface of the disc isshown in FIG. 3.

Referring to FIG. 3 as well as FIG. 2, the disc 42 has a plurality ofopaque, sector-shaped marks 43 (called lines herein for the sake ofconvenience) spaced arcuately around the disc 42. The angular width orthickness D of each opaque line 43 is the same. However, the spacing L LL etc. between adjacent lines 43 decreases gradually as one progressesin a counterclockwise direction from a starting line 47 to an endingline 49 which is somewhat less than 360 away from line 47. A relativelywide opaque sector 45 is provided between the line 47 and 49.

Referring again to FIG. 2, a light-emitting diode 68 (abbreviatedhereinafter LED) is positioned on one side of the disc 42 and shineslight through the transparent portions between the lines 43 of the discto a phototransistor 70 on the other side of the disc. The LED 68 andthe phototransistor 70 are located approximately at the positionindicated by the letter X in FIGS. 2 and 3.

The disc 42, the LED 68 and the phototransistor 70 serve two differentfunctions. First, they serve to indicate the position of the shutter 16during deceleration of the shutter, and also serve as part of apulsegenerating network which is used to control the energy to the drivemotor 40 and bring. it smoothly to a stop when the opaque region 45arrives at the point X. The angular position of the disc 42 relative tothe shutter 16 is set so that when the disc and shutter are stopped withthe portion 45 of the disc 42 at the point X, one of the blockingportions 32 of the shutter will be in the optical path between the lens14 and the film 20 to reflect instead of transmit images from the lens.

The LED 68 is connected through a resistor 72 to the upper contact of arelay 58. That same contact of relay 58 is connected through a resistor74 and a diode 76 to the input of an inverting amplifier 80 whose outputis connected to the base of a transistor 66.

The contacts of the relay 58 are normally open. Returning for a momentto the condition in which the camera switch 44 still is turned ON, 12volts DC is supplied through camera switch contact arm 48 and a lead 57to the collector of transistor 66 (as well as to other components of thesystem). At this time, the input to inverting amplifier 80 is at logiczero because there is a very low impedance path between the input ofamplifier 80 and ground. This path is through diode 76, resistors 72 and74, and the LED 68. LED 68 is not energized at this time since novoltage is applied to its anode. Since the input of amplifier 80 is atlogic zero, its output is at logic one, the transistor 66 is turned on,and the coil 60 of the relay 68 is energized so that the contact arms 62and 64 are forced against their respective contacts.

Now, when the camera switch 34 is turned to the OFF position, 12 voltsDC still is supplied to lead 57 through the contact arm 64 of relay 58,thus maintaining transistor 66 in a conducting state and latching therelay in its energized condition. Simultaneously, 12 volts also isapplied through contact arm 48 of switch 44 to the junction between theresistors 72 and 74, thus supplying a bias voltage for energizing theLED 68.

The light emitted by the LED 68 through the transparent regions betweenlines 43 on the disc 42 are converted into electrical pulses by thephototransistor 70. These pulses are sent to the input of an invertingamplifier 82 which is supplied through a bias resistor 84 from the line57. The amplifier 82 serves mainly as a pulseshaping circuit to providea clean rectangular wave output pulse.

The output of amplifier 82 is sent to a circuit including a diode 86connected in parallel with a resistor 88 which is connected in serieswith a variable resistor 90. This parallel combination is connected tothe upper terminal of a capacitor 92 whose lower terminal is groundedand also is connected to the input of another inverting amplifier 94.

When light from the LED 68 falls on the phototransistor 70, the input togate 82 falls to zero and its output rises from zero to 12 volts. Thecapacitor 92 starts charging to this voltage through the resistors 88and 90. Amplifier 94 is an inverting level-detector gate which switcheslogic states when its input voltage reaches approximately 6 volts. Thus,when the charge on the capacitor 92 reaches approximately 6 volts, theoutput of gate 94 goes from logic one to logic zero. The output of thisgate is sent to one input lead of a NOR circuit 100 whose output isconnected to the base of a transistor 102 whose output voltage is e,,.The voltage e is supplied to the motor control transistor 56 through acurrent-limiting resistor 104 and a diode 106. The output of gate 100will switch from logic zero to logic one if and only if the voltage atits second input 97 is below 6 volts.

When the output of gate 100 switches, the transistor 102 turns on andturns on transistor 56, thus supplying approximately 12 volts DC to themotor 40.

When an opaque line 43 once again blocks the light from reaching thephototransistor 70, the input voltage to the gate 82 suddenly goes high,and its output goes to zero. This causes the capacitor 92 to dischargerapidly through the diode 86 and the ground connection provided by thegate 82 when it is in its logic zero condi tion. Thus, the input voltageto gate 94 drops suddenly to zero and the output of gate 94 does high.This turns off the gate 100 and the transistors 102 and 56, thusdeenergizing the motor 40. The energy pulse thus delivered to the motor40 accelerates the motor by an amount sufficient to ensure that the disc42 will reach the next transparent region, except in the case when theend line 49 terminates the pulse to the motor.

For the purposes of the following explanation, assume that the speed ofthe disc 42 remains constant. When the next transparent region againappears, allowing light to again reach phototransistor from the LED 68,a 12 volt pulse to the motor 40 again is initiated, as before. However,since the spacing between adjacent opaque lines 43 has decreased, thetime duration of the resulting voltage pulse to motor 40 would decrease,with the result that the energy delivered by the pulse also decreases.However, the speed of the motor and disc actually decrease. Therefore,the time duration of the pulse to motor 40 is increased so that thisnext pulse is roughly the same in energy as was the previous pulse. Theenergy delivered to the motor thus is maintained at a level sufficientto ensure that the deceleration of the motor is not so great that thedisc 42 stops short of the desired location.

The foregoing procedure is repeated, with the pulses continuing to bedelivered to the motor 40 as the end point 49 on the disc approaches thepoint X marking the location of the LED 68 and the phototransistor 70.When this point is reached, the shutter and its motor 40 have sloweddown very considerably. As the opaque section 45 passes between the LEDand the phototransistor, no pulses can be delivered to the motor 40. Thedimensions of the portion 45 are such that, when the speed, inertia,bearing friction, etc. of the motor 40, the shutter 16, and the disc 42are taken into consideration, the motor and shutter will usually coastto a stop within the distance between points 49 and 47. Thus, theshutter 16 will stop with one of its blocking portions 42 in properposition to reflect instead of transmit images from the lens 14.

The foregoing operation is illustrated by the graph of FIG. 4, in whichthe output voltage e to the motor 40 and the charging voltage e of thecapacitor 92 are plotted against time. FIG. 4 illustrates the conditionin which, when the point 47 passes the point X, the speed of the disc 42is so low that it would coast to a stop long before the shutter reachesthe desired position. That is, FIG. 4 illustrates the condition in whichthe shutter enters its last revolution without enough speed to coast tothe desired position.

In FIG. 4, the times L L and L are the times between opaque lines 43relatively shortly after the starting point 47, midway around the disc,and near the end line 49 on the disc, respectively, as is indicated bythe corresponding distances L L and L in FIG. 3. The times D in FIG. 4represent the times taken by the lines 43 to pass the point X. Althoughthe angular width D of each of the sectors or lines 43 is the same, thetime D will not usually be constant because the disc slows downconsiderably during its rotation through one revolution. However, thevariation of D is relatively insignificant. It can be seen from FIG. 4that the time periods P P and P of the respective output pulses e, areprogressively shorter and thus contain pregressively less energy as thedisc rotates further.

The times L L and L and the pulse durations P P and P as shown in FIG.4, illustrate only the effects of the variable spacing between the lines43 on the disc 42. Not illustrated is the negative feed-back effectcreated by the fact that these time periods depend not only upon thespacing between adjacent lines 43 on the disc 42, but also upon thespeed of the disc. Thus, if the speed of the disc 42 increases, the timeperiod L between adjacent lines and the duration P of the resultingpulse decreases so as to decrease the energy delivered to the motor 40and allow it to slow somewhat. With a decrease in the speed of the disc42, the next time periods L and P will increase, thus increasing theenergy to the motor and accelerating it somewhat. Thus, the speed of thedisc and shutter are regulated to a value determined by the spacing ofthe lines 43 and the time constant TC of the circuit consisting ofresistors 88 and 90 and the capacitor 92.

The disc 42 and motor 40 may not always come .to a stop within 1revolution of disc 42. In fact, most camera motors now in use will notcoast to a stop in only one revolution, and usually require 4 to 10revolutions in which to stop. In accordance with another advantageousfeature of the invention, the spacing between lines 43 and the timeconstant TC are set at values such that the voltage e never reaches the6 volt level necessary to fire gate 94, with the result that no pulsesat all are developed, until the last revolution of the disc 42. Then,during that last revolution, if the speed of the disc is too low tobring it to the proper rest position, the operation of the circuit asshown in FIG. 4 will take place. The time constant TC can be adjusted bymerely adjusting the variable resistor 90. This will vary. the slope ofthe leading edges of the voltage pulses e shown in FIG. 4. If theresistance of the resistor is increased, the time constant for chargingthe capacitor 92 will be increased, and the pulses e will be of shorterduration and will contain less energy, or will be nonexistent. On theother hand, if the resistance of resistor 90 is decreased, the timeconstant for charging the capacitor 92 will decrease and the pulses e,will have a longer time duration and will contain more energy.

AUTOMATIC TURN-OFF From approximately 1 to 10 seconds after the cameraswitch 44 has been turned OFF, the circuit shown in FIG. 2 operatesautomatically to de-energize the relay 58 and completely deactivate themotor 40 and the circuit shown in FIG. 2.

When the camera switch 44 initially is turned OFF, the voltage suppliedto the junction between the resistors 72 and 74 back-biases the diode 76so that the capacitor 78 connected to the input of the gate 80 can startreceiving charging current from the line 57 through the resistors 96 and98. When the voltage at the input of gate 80 has charged up to 6 volts,the output of gate 80 returns to logic zero, and the transistor 66 turnsoff. This de-energizes the coil 60 to relay 58 and causes the contactarms 62 and 64 to return to their normally open positions. This removesthe voltage from the junction between resistors 72 and 74,- anddeenergizes the light-emitting diode 68. It also should be rememberedthat, should the gate still be operating, the appearance of 6 volts onits lead 97 also will turn off gate 100. This provides added safety.

The capacitor 78 now is free to discharge through the low-impedance paththrough diode 76, the resistor 72 and 74 and the LED 68, and the controlcircuit is ready again for further operation. The time constant of thecircuit including resistors 96 and 98 and the capacitor 78 determinesthe time it takes for the circuit to antomatically turn itself off. Ashas been noted above, this time typically varies between approximately 1and 10 seconds.

It is preferred that the LED 68 emit infrared radiation rather thanvisible light radiation. By using such an infrared LED, shielding neednot be used to prevent the film in the camera from being exposed byleakage from the LED. The phototransistor 70 should be responsive in theinfrared range of the spectrum. The light from the LED is focused by anintegral lens in the LED, and is limited to a fine, linear beam by meansof a mask (not shown) with a fine slit. The term light," as used herein,includes electromagnetic radiation throughout the spectrum, and,therefore, includes both visible and infrared radiation.

The foregoing system has been built and successfully operated using thefollowing electrical components:

Component Value or identification Resistor 90 l megohm potentiometerResistor 88 47,000 ohms Resistor 98 1.5 megohms Resistor 96 4.7 megohmsResistor 104 1,000 ohms Resistor 84 100,000 ohms Resistor 72 330 ohms,V; watt Resistor 74 [0,000 ohms Diodes 76, 86 and 106 Capacitor 92 .015microfarads Capacitor 78 L microfarads Gates 80, 82, 94 and 100 LED 68Phototransistor 70 The above-described speed control system can be usedto maintain the motor speed constant, as well as to control the speed ina deceleration mode of operation, by simply making the spaces betweenthe indicia 43 equal instead of decreasing magnitude, and by eliminatingthe opaque region 45 on the disc 42. This control arrangement can bequite useful as a simple device in controlling the speed of cameramotors such as those used in driving the zoom lens in the camera. Thespeed can be varied over a wide range simply by varying the setting ofthe time constant TC in the manner described above.

It should be made abudently clear that various other modifications canbe made in the specific structures disclosed herein without departingfrom the spirit and scope of the invention. For example, it should beclear that the disc 42 need not have the specific configuration shownand described herein. In place of the optical disc and detectordescribed, there can be used a disc in which conductive andnon-conductive segments replace the opaque lines 43 and the transparentspaces between them. A brush and electrical circuit connected to itcould be used to detect the presence of the conductive andnon-conductive segments as the disc rotates.

It also should be apparent that the indicia such as opaque marks 43 orconductive segments need not appear on a separate rotor such as the disc42 but, instead, can be formed integrally with the shutter 16 itself.For example, if there is room in the vicinity of the hub of the shutter16, the indicia can advantageously be placed directly on the hub so asto maximize accuracy of location, and minimize weight, bulk andmanufacturing expense.

In any event, the system described herein not only is accurate, but itis relatively simple in construction and relatively trouble-free.

I claim:

1. In a motion picture camera having a rotary shutter and drive meansfor rotating said shutter, shutter drive control means including meansfor delivering to said drive means electrical energy in an amountsufiicient to prevent said shutter from stopping before it reaches apre-determined rotational position, and for decreasing said energysubstantially to zero when said shutter reaches said pre-determinedrotational position so as to stop said shutter adjacent said position,said control means including a rotor with indicia spaced therearound,the spacing between said indicia decreasing progressively around saidrotor, means for coupling said rotor to said shutter for rotationtherewith, means for detecting said indicia as said rotor rotates andcontrolling said energy in accordance with the time between the passageof adjacent ones of said indicia past said detecting means.

2. Apparatus as in claim 1 in which said shutter has at least oneblocking portion which, when in an operative position, prevents imagesfrom reaching the film in said camera, and in which said energydecreases to zero when said blocking portion reaches said operativeposition.

3. Apparatus as in claim 1 in which said shutter has at least oneblocking portion which, when in an operative position, prevents imagesfrom reaching the film in said camera, and in which said blockingportion reflects said images hack to the eyepiece of said camera whensaid blocking portion is in said operative position.

4. A motion picture camera including a camera lens, a rotary reflectiveshutter, a film guide, a motor for driving said shutter, and controlmeans for stopping said shutter in a reflective position, said controlmeans including pulse generator means for selectively delivering to saidmotor electrical pulses each of whose energy varies directly with theangular distance of a first point on said shutter from a referencelocation, inversely with the speed of said shutter, and decreasessubstantially to zero when said shutter is adjacent said reflectiveposition.

5. A camera as in claim 4 including means for starting said pulsegenerator when said shutter reaches a first rotational position, andmeans for stopping said pulse generator when said shutter reaches asecond rotational position at which said first point has reached saidreference location and said shutter is adjacent said reflectiveposition.

6. A camera as in claim 5 in which said pulse generator includes a rotorwhich rotates with said shutter, said rotor having arcuately spacedlinear indicia thereon, the spacing between said indicia decreasingbetween a first line corresponding to said first rotational position ofsaid shutter and a second line corresponding to said second rotationalposition of said shutter, and a detector positioned to detect saidindicia and produce said pulses in response thereto.

7. A camera as in claim 6 including charge storage means for storingcharge to develop pulses in the time intervals between passage ofadjacent ones of said indicia past said source and said detector.

8. In a motion picture camera having a rotary shutter, a drive motor forrotating said shutter, shutter drive control means including a rotorcoupled to rotate with said shutter, said rotor having indicia angularlyspaced thereon, means for detecting said indicia and producingelectrical pulses in response to the detection of said indicia, saidindicia being spaced progressively closer together around said rotor ina predetermined direction, means for energizing said motor with saidpulses, and means for substantially stopping said pulses when said rotoris near a pre-determined position in which said shutter prevents imagesfrom reaching the film in said camera.

9. Apparatus as in claim 8 in which said indicia are opaque regions withtransparent regions between said opaque regions on said rotor, saiddetecting means including a radiation source and a radiation-responsivedetector device positioned to receive radiation from said source throughsaid transparent regions.

10. Apparatus as in claim 9 in which said radiation source is alight-emitting diode and said radiationresponsive detector device is aphototransistor.

11. Apparatus as in claim 9 in which the angular extent of saidtransparent regions between said opaque regions decreases to zero froman initial value at a starting position when said rotor rotates in saidpredetermined direction past said source and detector device, andelectrical charge storage means operated by said detector device fordeveloping said pulses, the amount of energy in each pulse beingdetermined by the charge stored in said storage means.

12. Apparatus as in claim 11 including on said rotor an opaque region ofrelatively great angular extent between said starting position and theposition at which the angular extent of the transparent spaces drops tozero.

13. A device as in claim 8 including means for setting a minimum motorspeed above which said electrical pulses are not produced.

14. A device as in claim 13 in which the detecting means includes chargestorage means for storing charge between adjacent ones of said indicia,and level detector means for detecting the level of charge on saidstorage means and starting one of said electrical pulses when the chargereaches a pre-determined level.

1. In a motion picture camera having a rotary shutter and drive meansfor rotating said shutter, shutter drive control means including meansfor delivering to said drive means electrical energy in an amountsufficient to prevent said shutter from stopping before it reaches apre-determined rotational position, and for decreasing said energysubstantially to zero when said shutter reaches said pre-determinedrotational position so as to stop said shutter adjacent said position,said control means including a rotor with indicia spaced therearound,the spacing between said indicia decreasing progressively around saidrotor, means for coupling said rotor to said shutter for rotationtherewith, means for detecting said indicia as said rotor rotates andcontrolling said energy in accordance with the time between the passageof adjacent ones of said indicia past said detecting means.
 2. Apparatusas in claim 1 in which said shutter has at least one blocking portionwhich, when in an operative position, prevents images from reaching thefilm in said camera, and in which said energy decreases to zero whensaid blocking portion reaches said operative position.
 3. Apparatus asin claim 1 in which said shutter has at least one blocking portionwhich, when in an operative position, prevents images from reaching thefilm in said camera, and in which said blocking portion reflects saidimages back to the eyepiece of said camera when said blocking portion isin said operative position.
 4. A motion picture camera including acamera lens, a rotary reflective shutter, a film guide, a motor fordriving said shutter, and control means for stopping said shutter in areflective position, said control means including pulse generator meansfor selectively delivering to said motor electrical pulses each of whoseenergy varies directly with the angular distance of a first point onsaid shutter from a reference location, inversely with the speed of saidshutter, and decreases substantially to zero when said shutter isadjacent said reflective position.
 5. A camera as in claim 4 incLudingmeans for starting said pulse generator when said shutter reaches afirst rotational position, and means for stopping said pulse generatorwhen said shutter reaches a second rotational position at which saidfirst point has reached said reference location and said shutter isadjacent said reflective position.
 6. A camera as in claim 5 in whichsaid pulse generator includes a rotor which rotates with said shutter,said rotor having arcuately spaced linear indicia thereon, the spacingbetween said indicia decreasing between a first line corresponding tosaid first rotational position of said shutter and a second linecorresponding to said second rotational position of said shutter, and adetector positioned to detect said indicia and produce said pulses inresponse thereto.
 7. A camera as in claim 6 including charge storagemeans for storing charge to develop pulses in the time intervals betweenpassage of adjacent ones of said indicia past said source and saiddetector.
 8. In a motion picture camera having a rotary shutter, a drivemotor for rotating said shutter, shutter drive control means including arotor coupled to rotate with said shutter, said rotor having indiciaangularly spaced thereon, means for detecting said indicia and producingelectrical pulses in response to the detection of said indicia, saidindicia being spaced progressively closer together around said rotor ina predetermined direction, means for energizing said motor with saidpulses, and means for substantially stopping said pulses when said rotoris near a pre-determined position in which said shutter prevents imagesfrom reaching the film in said camera.
 9. Apparatus as in claim 8 inwhich said indicia are opaque regions with transparent regions betweensaid opaque regions on said rotor, said detecting means including aradiation source and a radiation-responsive detector device positionedto receive radiation from said source through said transparent regions.10. Apparatus as in claim 9 in which said radiation source is alight-emitting diode and said radiation-responsive detector device is aphototransistor.
 11. Apparatus as in claim 9 in which the angular extentof said transparent regions between said opaque regions decreases tozero from an initial value at a starting position when said rotorrotates in said predetermined direction past said source and detectordevice, and electrical charge storage means operated by said detectordevice for developing said pulses, the amount of energy in each pulsebeing determined by the charge stored in said storage means. 12.Apparatus as in claim 11 including on said rotor an opaque region ofrelatively great angular extent between said starting position and theposition at which the angular extent of the transparent spaces drops tozero.
 13. A device as in claim 8 including means for setting a minimummotor speed above which said electrical pulses are not produced.
 14. Adevice as in claim 13 in which the detecting means includes chargestorage means for storing charge between adjacent ones of said indicia,and level detector means for detecting the level of charge on saidstorage means and starting one of said electrical pulses when the chargereaches a pre-determined level.